1. Field of the Invention
The present invention relates to a monostable permanent magnetic actuator using a laminated steel core, and particularly, to an actuator to operate a circuit breaker, a switch, etc. of power equipment.
2. Background of the Invention
As an actuator for power equipment, a spring mechanism, and a hydraulic or pneumatic actuator are generally used. However, the actuator has a large number of components, and has to control mechanical energy so as to obtain an adjustment force. Accordingly, the actuator has a complicated structure, and requires to be repaired.
In order to solve these problems, the conventional mechanism has been replaced by an actuator using permanent magnets and electric energy in the power equipment. The permanent magnetic actuator is configured such that a mover thereof is held at a stroke using magnetic energy of the permanent magnets, and electric energy is applied to a coil to move the mover to a stroke.
The permanent magnetic actuator may be categorized into a bistable type and a monostable type depending on a mechanism that the mover is held at a preset position. The bistable type permanent magnetic actuator is configured such that a mover can be held at both ends of a stroke due to permanent magnets, whereas the monostable type permanent magnetic actuator is configured such that a mover is held at only one of both ends of a stroke. The mover of the bistable type permanent magnetic actuator is held at a preset position by magnetic energy of permanent magnets upon opening or closing power equipment. Accordingly, the bistable type permanent magnetic actuator is more advantageous than the monostable type requiring for a separate maintenance mechanism, in that it can perform the closing/opening operation without a mechanical component such as a spring.
On the contrary, the monostable type actuator has the following advantages. Firstly, power equipment can be closed or opened by using one coil.
Secondly, the monostable type actuator is mounted with an open spring, thereby opening power equipment without an additional energy storage device (e.g. spring) in an opening device for an emergent case.
Thirdly, differently from the bistable type actuator, a closing or opening operation is implemented by one coil. This may allow a driving coil to have a large number of windings thereon. Since driving energy is proportional to a stroke, the mover of the monostable permanent magnetic actuator can be fabricated so as to have a long stroke.
FIGS. 1 and 2 are sectional views of an actuator in accordance with the conventional art. The actuator 10 of FIG. 1 comprises a middle cylinder 12 having a cavity, and a lower cylinder 14 coupled to a lower side of the middle cylinder 12. A close coil 18 for applying a downward magnetic force to the mover 16 by receiving external power is installed below the middle cylinder 12. An upper cylinder 20 is coupled to an upper side of the middle cylinder 12. And, permanent magnets 22 for applying a downward magnetic force to the mover 16 are installed on an upper surface of the upper cylinder 20.
An open coil 24 for forming an attenuating magnetic force (i.e., a magnetic force opposite to a magnetic force from the permanent magnets 22) by external power is positioned on a bottom surface of the upper cylinder 20. And, an open spring 26 for applying an upward elastic force to the mover 16 is installed on a bottom surface of the lower cylinder 14.
Referring to FIG. 1, the permanent magnets 22 are in a state to apply an attractive force to the mover 16, and the open spring 26 is in a compressed state to apply an upward elastic force. However, the elastic force of the open spring 26 is less than the magnetic force of the permanent magnets 22, the mover 16 maintains a downward moved state as shown in FIG. 1. Under this state, once power is supplied to the open coil 24, a magnetic force is generated in an opposite direction to the magnetic force of the permanent magnets 22. Accordingly, the magnetic force of the permanent magnets 22 is attenuated, and thereby the elastic force of the open coil 24 becomes relatively larger. As a result, the mover 16 is upwardly moved as shown in FIG. 2.
Then, power to the open coil 24 is cut off, and power is supplied to the close coil 18. This allows the magnetic force of the permanent magnets 22 and the close coil 18 to become relatively larger than the elastic force of the open spring 26. Accordingly, the mover 16 maintains the downward moved state as shown in FIG. 1.
However, the conventional monostable permanent magnetic actuator has the following problems.
Firstly, when power is supplied to the close coil or the open coil so as to upwardly or downwardly move the mover 16, an eddy current is generated by drastic change of a magnetic flux. This eddy current generates force in an opposite direction to the moving direction of the mover 16, thereby lowering the operation of the mover 16. Furthermore, this eddy current causes the actuator to have a long operation time and large operation energy, thereby badly influencing on the actuator.
Secondly, the middle cylinder and the lower cylinder undergo mechanical processes to have cylindrical shapes. Here, the mechanical processes are performed with high costs.
Thirdly, since a magnetic force to downwardly move the mover is applied only to an upper plate of the mover, it is difficult to obtain a sufficient attractive force.